1. Field of the Invention
The present invention relates to a sheet feeder provided with a sheet conveyance guide mechanism used in an image forming apparatus such as a printer, a copier, a facsimile machine or a complex machine having multiple functions of these, and an image forming apparatus provided with this sheet feeder.
2. Description of the Related Art
Conventionally, as sheet feeders used in image forming apparatuses such as printers, copiers, facsimile machines and complex machines having multiple functions of these, those which can be detachably mounted into apparatus main bodies and which are provided with sheet cassettes for storing a plurality of transfer sheets have been widely used.
For sheet cassettes to be used in the foregoing image forming apparatus, for example, a sheet cassette 113 shown in FIG. 10 may be adopted. As shown in FIG. 10, the sheet cassette 113 is in the form of a drawer so that transfer sheets can be replenished and exchanged by pulling out the sheet cassette 113 from the image forming apparatus main body.
The sheet cassette 113 is provided with a storing section 101 for storing therein transfer sheets, a lifter plate 102 for lifting the transfer sheets stored in the storing section 101 along a sloping face in a sheet feeding direction (upward in FIG. 10), a separation roller 103 disposed downstream of the lifter plate 102 in a transport direction, a transfer sheet guide 104 provided around the separation roller 103 in such a manner as to expose an upper end portion of the separation roller 103 and inclined upwardly in the transport direction, and transport rollers 105 disposed downstream of the transfer sheet guide 104.
As shown in FIG. 11, a pickup roller 106 is disposed above (on side where the transfer sheets are to be placed) a downstream end of the lifter plate 102 in the transport direction. The separation roller 103 and the transport rollers 105 of the sheet cassette 113 shown in FIG. 10 are arranged to respectively face a feed roller 107 and a transport roller 108 in a state where the sheet cassette 113 is mounted in the apparatus main body (overall view is not shown).
The transfer sheets placed on the lifter plate 102 are fed one by one from the uppermost one by the rotations of the pickup roller 106 with the uppermost one pressed against the pickup roller 106, and are conveyed to pass between the feed roller 107 and the separation roller 103. Only the uppermost one of the transfer sheets as fed by the pickup roller 106 passes between the transport rollers 105 and 108 and is transported to an image forming section (not shown) provided in the apparatus main body by the rotations of the feed roller 107 in the transport direction and the rotations of the separation roller 103 in a direction opposite to the transport direction. At this time, the transfer sheet is guided by the transfer sheet guide 104.
Here, a downstream end in the transport direction of the transfer sheet as fed by the pickup roller 106 may hang down in some cases due to softness peculiar to the transfer sheet as shown in FIG. 11. If the leading end of the transfer sheet hangs down from an upper surface 104a (guide face) of the transfer sheet guide 104 in this way, it collides with a vertical wall surface 101a of the storing section 101 to create a hitting sound. Further, if the transfer sheet having collided with the vertical wall surface 101a enters a clearance between the transfer sheet guide 104 and the vertical wall surface 101a without being placed on the upper surface 104a of the transfer sheet guide 104, a sheet jam is liable to occur, which creates a large impact sound.
In view of this problem, Japanese Unexamined Patent Publication No. 2003-307890 (date of publication: Oct. 31, 2003) discloses a noise eliminating mechanism capable of easily adjusting noise according to a noise source.
Japanese Unexamined Patent Publication No. H11-188946 (Patent No. 3605786) (date of publication: Jul. 13, 1999) discloses technology for suppressing the leakage of noise to the outside by effectively sealing a clearance between an automatic duplex unit (ADU) and an ADU cassette.
Further, Japanese Unexamined Patent Publication No. H07-309465 (Patent No. 3448097) (date of publication: May 19, 1994; corresponding U.S. Pat. No. 5,584,475) discloses technology for reducing noise generation by arranging a noise eliminating member made of a material having a small coefficient of friction downstream of a separation pad made of a material having a large coefficient of friction in a transport direction and arranging the circumferential surface of a feed roller to cross over the separation pad and the noise eliminating member.
However, any of the above prior art documents merely discloses the technology for reducing noise generation and therefore fails to fundamentally solve a problem of a transfer sheet conveyance failure, which causes the generation of noise and a jam. This problem has been particularly difficult to solve in the case of using thick transfer sheets or hard transfer sheets.